1. Field of the Invention
The invention relates to a method of decoding possibly mutilated code words of a code, wherein an information word and an address word are encoded into a code word of said code using a generator matrix, and wherein said address words are selected such that address words having a known relationship are assigned to consecutive code words. The invention relates further to a corresponding apparatus for decoding possibly mutilated code words and to a computer program for implementing said method.
2. Description of the Related Art
In European Patent Application No. 01201841.2, corresponding to U.S. Patent Application Publication No. 2003/0066014-A1 (PHNL 010331), the concept of coding for informed decoding is described. An enhancement can be found in European Patent Application No. 01203147.2, corresponding to U.S. Patent Application Publication No. 2003/0095056-A1 (PHNL 010600). The key element of the inventions described in these applications is an appropriate selection of the mapping of information strings towards code words from the Error Correcting Code (ECC) that is applied. The aim of coding for informed decoders is to enable more reliable information retrieval if the decoder a priori knows part of the encoded information. A typical example is in the field of address retrieval of optical media. In case of a forced jump to a certain sector, part of the address of the sector in which the read/write head will land is known taking the jump accuracy into account. For instance, in DVR (Digital Video Recording), it is anticipated that on the spiral track on the optical disc, a series of messages is encoded which aids in the logical positioning of the read/write head above the disc, which, e.g., contains copyright information, date information and a logical track counter. Of this information, only the logical track counter changes in between successive messages. Therefore, a priori known information can be available from successful decoding of previous messages.
According to the solutions described in the above-mentioned patent applications, decoding of a second message can only gain from the decoding of the first message, if said first decoding is successful. A second decoding can then, in turn, aid in the decoding of the third message, and so on. However, if the decoding of the first message fails, the fact that the second message has been encoded in a special way does not improve the error correcting capabilities, i.e., the second and any further decoding is not helped by previous decodings. All decodings could then fail. In other situations, for example, at the very start of a recording or playback session, not much is known about the actual landing place of the read/write head. In that case, only the error correcting capabilities of the code can be used for retrieving information.